This invention relates to a centrifuge rotor of the type adapted to deposit particles suspended within a supernatant onto a deposition surface and, in particular, to a chamber block for such a rotor having a recess provided therein adapted to receive an absorbant plug.
The centrifuge rotor arrangement such as that described in U.S. Pat. No. 4,423,699 and in U.S. Pat. No. 4,314,523, both assigned to the assignee of the present invention is adapted to deposit, or sediment, particles, such as blood cells, suspended in a liquid medium known as a supernatant onto a suitable deposition surface, such as a microscope slide, so that further examination of the cells may occur.
Each rotor arrangement is adapted to receive a plurality of removable chamber blocks therein. Each chamber block is provided with an inlet orifice communicating with an inlet channel for receiving a sample containing a supernatant having particles suspended therein and an outlet channel through which the particles and supernatant are moved under the influence of centrifugal force toward the deposition surface. A supernatant withdrawal conduit, or cannula, extends through the body of the chamber block. Supernatant is collected by withdrawing the same under suction in a direction rearwardly from the deposition surface. Exemplary of chamber blocks usable with the rotors having a vacuum source incorporated therewith are those described and claimed in U.S. Pat. No. 4,306,514 (Bouclier) and U.S. Pat. No. 4,327,661 (Boeckel).
Other techniques are known in the art for withdrawing excess supernatant from the vicinity of the deposition surface. For example, a device sold under the name of "Cytospin" by Shandon Elliott utilizes a bowl-type centrifuge rotor whose outer periphery defines a vertical wall adapted to receive microscope slides. Chambers for holding samples to be sedimented are positioned radially against the slides with a piece of filter paper disposed between each chamber and its associated slide. A hole in the filter paper is positioned over the outlet orifice of the chamber such that cells and the supernatant when centrifuged are driven against the slides. Capillary force of the filter paper and centrifugal force facilitate the withdrawal of excess fluid from the surface of the slide by forcing the excess liquid into the filter paper. Unfortunately, however, the filter paper can have a deleterious effect in that it tends to absorb the fluid so rapidly cells are literally "sucked" into the peripheral edges of the filter paper surrounding the outlet orifice with relatively few cells having sufficient time to pellet or sediment against the slide itself. For this reason the cells tend to run dry.
Accordingly, it would be desirable to provide a chamber block for use with a centrifuge rotor of the type for sedimenting cells against the deposition surface that avoids the use of filter paper between the chamber block and the deposition surface and the use of suction to withdraw the supernatant rearwardly from the deposition surface.